The use of radioisotopes for the treatment of disease such as cancer dates back to the beginning of the 20th century. In particular, localized radiotherapy has become a standard treatment option for many cancers. To confine the radiation to tumor sites, two general approaches are currently used in clinical practice: (1) systemic radioisotope therapy using radiopharmaceuticals and (2) “sealed source” radiotherapy or brachytherapy. In the first approach, radioactive constructs are administered to a patient systemically. The administered constructs then target tumors through metabolism or specific biological events. Radionuclides emitting β-particle, α-particle, or Auger electrons have been used in this approach. Unfortunately, the targeting efficacy and retention rate of many radioactive drugs inside tumor sites remain major challenges. The undesired uptake of radiopharmaceuticals by normal tissue also remains a problem with the systemic radiotherapy approach.
In brachytherapy, radioactive sources are placed into or next to the tumor volume. In previous brachytherapy methods, radioisotopes are encapsulated in a millimeter sized metal container or capsule to ensure the radiation sources remain in a desired location, such as the implantation site. In addition, gamma or X-ray emitting radioisotopes are typically used in previous brachytherapy methods due to the need to penetrate the metal capsule. For clinical applications, the brachytherapy capsules or “seeds” are permanently placed in the tumor through a surgical procedure. The radiation emitted from the brachytherapy seeds is thus used to treat the tumor “from the inside out,” without traversing as much normal tissues as in external radiation therapy. However, the surgical implantation of millimeter sized brachytherapy seeds can cause many adverse side effects and greatly limits the application of brachytherapy for different tumor types, sizes, and locations.
Therefore, there remains a need for improved radioactive compositions, including for medical applications such as the radiation treatment of disease.